The present invention relates to a power supply device and an arc machining power supply device that includes an inverter circuit, which converts alternating current (AC) power from a commercial power into direct current (DC) voltage and then converts the DC voltage to a predetermined AC voltage, and are applicable to input power including a plurality of different voltage values.
Japanese Laid-Open Patent Publication No. 2009-17656 describes an example of a power supply device for an arc machine or the like that includes a DC converter circuit, which converts AC voltage to DC voltage, and an inverter circuit, which converts the DC voltage to AC voltage. The DC converter circuit includes a rectifier circuit, which rectifies commercial power (three phase AC power) and a smoothing capacitor, which smoothes the rectified DC voltage. The inverter circuit includes a bridge circuit of a plurality of switching elements (first to fourth switching elements). The inverter circuit synchronously controls the activation and deactivation of a predetermined combination of the switching elements to convert the DC voltage from the DC converter circuit into a predetermined high frequency AC voltage. The predetermined high frequency AC voltage from the inverter circuit is further converted into machining DC voltage that is suitable for arc machining such as arc welding and arc cutting.
The power supply device includes a switching switch that switches between an internal operation of a specification corresponding to a commercial power of 200 V (200 V series) and an internal operation of a specification corresponding to a commercial power of 400 V (400 V series).
Specifically, an auxiliary switching circuit is arranged between the DC converter circuit and the inverter circuit. The auxiliary switching circuit includes an auxiliary capacitor, which is connected between two power lines at the upstream side of the inverter circuit. Further, the auxiliary switching circuit includes, between the DC converter circuit and the auxiliary switching circuit, fifth and sixth switching elements, which are arranged in the two power lines, and seventh and eighth switching elements, which are connected in series between the two power lines. The DC converter circuit includes a smoothing capacitor, namely, first and second smoothing capacitors connected in series between the two power lines in the present embodiment. The switching switch is connected between a first node of the first and second smoothing capacitors and a second node of the seventh and eighth switching elements. The switching switch connects and disconnects the first node and the second node.
When the commercial power of 200 V is supplied (hereinafter referred to as the 200 V series input), the switching switch disconnects the first node and the second node and supplies the inverter circuit with the voltage applied to the two ends of the first and second smoothing capacitors that are connected in series. When the commercial power of 400 V is supplied (hereinafter referred to as the 400 V series input), the switching switch connects the first node and the second node. As a result, by activating and deactivating a predetermined combination of the fifth to eighth switching elements, the voltage applied to the two ends of the first smoothing capacitor and the voltage applied to the ends of the second smoothing capacitor are alternately supplied to the inverter circuit. In this manner, the same DC voltage is supplied to the inverter circuit regardless of the voltage value of the input power.
In the auxiliary switching circuit, a soft switching control is performed to deactivate predetermined ones of the fifth to eighth switching elements before deactivation of the first to fourth switching elements of the inverter circuit. This switches each element with a zero voltage and zero current thereby reducing switching loss.
When controlling the inverter circuit, a typical pulse width modulation control (PWM control) is performed to adjustment the output of the power supply device to an extremely small level. In such a case, a control pulse signal provided to the switching elements of the inverter circuit and the auxiliary switching circuit, which is operated in cooperation with the inverter circuit, is set to have an extremely narrow on pulse width. This may hinder the activation of the switching elements and lead to shortcomings such as output instability and biased magnetism. It is thus desired that the output of the power supply device be stabilized while using PWM control.
One aspect of the present invention is a power supply device including a DC converter, and inverter circuit, an auxiliary switching circuit, a pulse width modulation circuit, a phase shift control unit, and a control switching unit.
The DC converter circuit includes a rectifier circuit and first and second smoothing capacitors, which are connected in series and arranged between two power lines at an output side of the rectifier circuit. The DC converter circuit rectifies and smoothes input AC power and converts the input AC power into DC voltage.
The inverter circuit includes a bridge circuit of first to fourth switching elements. Predetermined sets of the first to fourth switching elements are alternately activated and deactivated to convert the DC voltage to a predetermined AC voltage.
The auxiliary switching circuit includes an auxiliary capacitor, which is connected between the two power lines between the DC converter circuit and the inverter circuit, fifth and sixth switching elements respectively arranged on the two power lines between the DC converter circuit and the auxiliary capacitor, seventh and eighth switching elements connected in series between the two power lines between the auxiliary capacitor and the first and sixth switching elements, and a switching unit that connects or disconnects a first node of the first and second smoothing capacitors and a second node of the seventh and eighth switching elements.
The switching unit disconnects the first and second nodes when the input AC power has a first voltage value to supply a voltage across two terminals of the first and second smoothing capacitors to the inverter circuit. The switching unit connects the first and second nodes when the input AC power has a second voltage value that is two times greater than the first voltage value so that soft switching control is performed by activating and deactivating predetermined sets of the fifth to eighth switching elements, alternately supplying the inverter circuit with a voltage across the terminals of the first or second smoothing capacitor, and deactivating a predetermined one of the fifth to eighth switching elements before the first to fourth switching elements are deactivated to stop the voltage supplied to the inverter circuit.
The pulse width modulation control unit adjusts an on pulse width of a control pulse signal provided to the first to fourth switching elements and adjusts an on pulse width of a control pulse signal provided to the fifth to eighth switching elements in accordance with the adjusted width.
The phase shift control unit adjusts a phase difference of two control pulse signals provided to the same set of switching elements in the first to fourth switching elements or adjusts a phase difference of two control pulse signals provided to predetermined ones of the first to fourth switching elements and corresponding ones of the fifth to eighth switching elements.
The control switching unit operates the pulse width modulation control unit when a relatively large output is requested and operates the phase shift control unit when a relatively small output is requested.